1. Field of the Invention
The present invention relates to a method of mechanically breaking a parallel scribed or scored workpiece of brittle fracturing material, especial flat glass, in two cutting directions that are perpendicular to each other, by breaking tools. One breaking tool is a breaking roller used to break along one cutting direction and the other breaking tool is a breaking bar used to break along the other cutting direction.
2. Related Art
Small rectangular flat glass elements are necessary for numerous technical applications.
Small containers, which are closed on at least one side completely or partially by a thin glass pane, are used for housing micro- and opto-electronic components, such as quartz oscillators, SAW filters and CCD components in so-called “electronic packaging”. Frequently also housing covers made from thin glass panes are used for housing of micro-opto-electronic and opto-electronic components. The thickness s of these small thin glass panes is typically in a range from 10 μm≦s≦500 μm.
Small thin glass panes are also used as structural parts in the manufacture of micro-electronic and micro-mechanical components. Thus, for example, a quartz oscillator positioned between two thin glass sheets and connected with them is known from DE 196 49 332.
Thin glass panes used as closure elements of housings for micro-and opto-electronic components and structural parts of micro-electronic and micro-mechanical components are attached typically by gluing or soldering. Metal or glass solder is used as the joining material in the case of soldering. Glass solder is used in the majority of applications.
The manufacture of small rectangular glass panes for displays of electronic units, such as mobile phones, digital cameras, etc., is an especially interesting application. The so-called display cell, which comprises two glass panes glued to each other, plays a special role. The one glass pane is a TFT substrate (thin film transistor) and the other is the CF substrate (color front). These glass substrates typically are borosilicate glass with a thickness of between 0.2 and 1.1 μm.
The economical manufacture of this sort of small rectangular glass pane occurs according to the state of the art by dividing or breaking apart a larger rectangular flat glass plate or slab, as described for example in DE 100 16 628 A1. Edge quality requirements have become more stringent, since that has a decisive influence on the strength of the resulting small rectangular glass panes.
However the display cells are also made in a corresponding way by dividing a large double flat glass plate, as described, e.g., in U.S. Pat. No. 4,277,143. Up to 200 display cells, which correspond in size to the display format for a mobile phone, can be cut out of the double flat glass plate according to the layout.
A laser beam is currently used to a large extent to cut the respective flat glass plates into rectangles. This technique is widely known and does not need to be described in further detail here. Reference is made here to EP 0 872 303 A2, U.S. Pat. No. 5,609,284 and EP 0 062 484 A1 for this purpose. The cutting is basically performed by guiding a laser beam with a following cooling spot by means of a scanner linearly along a provided dividing line on a flat glass plate so that the glass is not cut through, but is only scribed up to a predetermined depth by inducing a thermo-mechanical stress. The scribing occurs first completely in a coordinated direction and after that in the other perpendicular direction. Subsequently the glass plate is mechanically broken along the scribed lines, typically by a machine, as it rests on a so-called breaking table.
In the case of a double flat glass plate first the one flat glass plate and subsequently the other flat glass plate are scribed and broken in order to make display cells.
The breaking along the perpendicular dividing or cutting directions takes place sequentially, advantageously according to DE 102 57 544 A1, i.e. each flat glass plate is first broken along the scribed lines by the second cutting device and subsequently along the scribed lines by the first cutting device. It has been shown that glass plates can be divided into the described small rectangular elements with a higher broken edge quality and higher yield with this breaking technique.
The machine breaking of the scribed flat glass plate occurs in a known manner by means of a so-called breaking bar in connection with a breaking roller according to US Published Patent Application 2005/0061123 A1. This sort of breaking bar comprises a longitudinally extended metallic blade with knife edge on one side, to which typically a different material, e.g. hard rubber, is applied so that the glass is not damaged.
The breaking force of the breaking bar, which is pressed successively using a mechanized breaking apparatus with controlled force along the scribed line on the scribed glass plate under stress with the scribed side on the breaking table, is comparatively large, so that the glass breaks comparatively “hard” due to the exerted “impacts”. In the known case a very long breaking bar is used, which extends over the entire width and/or length of the flat glass plate to be broken into separate pieces. Since the dimensions of the flat glass plate to be divided and/or the double flat glass plate are always increasing in the interest of greater efficiency, the metallic blade of the breaking bar becomes correspondingly longer, which impairs the maintenance of the required cutting accuracy, which is in a range from 5 to 10 μm. In the known case the breaking occurs along one dividing or cutting direction by means of the breaking roller and the breaking occurs along the other dividing or cutting direction by means of the breaking bar.